Single-phase speed regulating brushless direct current motor has advantages on energy efficiency and noise control, and has a wide range of application and, particularly, applications and environments including electronics, where energy efficiency and noise control are often of paramount consideration. In particular, these motors are often employed with cooling fans in consumer electronics equipment, such as for computer hard drives, data storage devices, video game consoles, CD/DVD players, and the like, which generally dissipate a lot power and generate a lot of heat while in operation.
Among the existing technologies regularly utilized in controlling the rotation speed of brushless direct current motor for cooling fans, there are three main methods for regulating the motor rotation speed: fixed speed; variable speed controlled by a clock signal, such as, a pulse width modulation (“PWM”) signal; and variable speed controlled by a temperature feedback.
Fixed speed fans are not able to vary the rotation speed, which is energy inefficient and cause more noise. For example, in a typical computer housing, there is a fixed speed cooling fan that operates continuously once the computer is turned on. The fixed speed cooling fan operates at its maximum power and does not meet the trend towards low-power consuming devices.
Variable speed fans are controlled by a clock signal, for example, a PWM signal and, generally have a fan speed that is near linear with the duty cycle of the PWM signal. For example, a device can use a PWM signal with specific duty cycle setup according to different operation mode to control the cooling fan. Therefore the cooling fan can work at low speed with respect to low work-load operation mode. Such designs are more energy efficiency and reduce noise; however, they may not offer as much efficiency and flexibility as may be desired.
Variable speed fans are controlled by a temperature feedback such as, a detected temperature of a component such as a power supply of an electric device, a processor, a memory, a hard disk drive, and the like. This temperature measurement is used to determine the rotational speed of the motor coupled to a cooling fan. This method provides more flexibility and reduce power consumed by the fan and motor and significantly reduces the noise generated by operation of the fan and motor when the detected temperature is relatively low. Fan and motor control based on temperature alone, however, presents a number of drawbacks because the fan speed control is reactive, rather than proactive. In other words, adjusting fan speed based on temperature only adjusts the fan speed after the temperature has already increased. When power dissipation is increased in a component, it takes time for the thermal information being transferred from the heat generating device to reach a temperature sensor. In this situation, desired cooling function may not be provided before the device reaches a still higher temperature or even reaches an undesirable temperature. In addition, other components in a system may also be heating up and the total heating of the system may not be linear with the temperature of the component where temperature is detected.
Therefore, it would be desirable to have a system and method for regulating the motor rotation speeds with a more robust, energy-efficient, flexible, yet not overly-complex, method of control.